An add-on is an optional or required additional charge attached to a subscription plan, separate from the plan's base price.
Businesses use add-ons to sell extra products, services, seats, or usage alongside a core subscription instead of forcing every combination into its own plan. Because an add-on is priced and configured on its own, a business can offer many variations of a subscription while keeping the plan catalog small.
What add-ons mean
An add-on has its own set of properties, independent of the base plan it is attached to:
Add-on code: a unique identifier used in API calls. It cannot be changed after creation.
Pricing model: fixed, tiered, volume, or stairstep, which determines how the charge is calculated per billing period.
Default quantity: the quantity included by default, which can be overridden at subscription creation if editable quantity is enabled.
Optional or required: whether the subscriber must include the add-on or can leave it off.
Billing timing: flat add-ons bill each period alongside the base charge, while usage-based add-ons bill in arrears after usage is reported.
Because these properties are set at the add-on level rather than the plan level, a single plan can carry multiple add-ons, each with its own pricing model and billing behavior.
Why add-ons matter
Add-ons let a subscription business grow revenue from existing customers without creating a new plan for every possible combination of features or usage. A customer can start on a base plan and add exactly what they need, and the business can price that incremental value separately from the core subscription.
This also keeps a plan catalog manageable. Instead of maintaining a separate plan for every seat count, storage tier, or optional feature, a business keeps one base plan and layers add-ons on top, each configured with the pricing model that fits it best.
Recurly supports four add-on pricing models (fixed, tiered, volume, and stairstep) plus usage-based billing with configurable aggregation, so a merchant is not limited to a single way of charging for optional extras. An add-on can be built from scratch on a specific plan, or derived from an item in a shared item catalog so the same definition can be reused across multiple plans instead of being redefined for each one.
How add-ons work
Setting up a quantity-based add-on generally follows this sequence:
Choose a pricing model: fixed, tiered, volume, or stairstep.
Add the add-on to a plan. Quantity-based pricing is configured at the add-on level, not the plan level.
Define the tiers and prices for that add-on, if using tiered, volume, or stairstep pricing.
Assign a quantity to the add-on when creating or updating a subscription.
The billing system calculates the correct charge automatically based on the configured pricing model and the assigned quantity.
The four pricing models behave differently even for the same quantity:
Fixed: a flat price per billing period, regardless of quantity.
Tiered: each unit is priced according to the tier it falls into. For example, the first 100 units might be priced at one rate and every unit after that at a lower rate.
Volume: all units are priced at the rate of the highest tier reached. If a customer's total quantity crosses into a discounted tier, that discounted rate applies to every unit, not just the ones above the threshold.
Stairstep: a flat price applies to an entire quantity range, regardless of how many units fall within that range. A customer with 25 units and a customer with 50 units in the same range pay the identical flat price.
Add-ons can also be usage-based rather than quantity-based, charging by a unit amount per unit of usage logged, or by a percentage of a monetary usage amount. Usage-based add-ons use one of two calculation methods: Cumulative, which sums every usage record logged during the billing period and suits consumption-based metrics, or Last Recorded, which bills based only on the most recent usage record and suits state-based metrics like a current seat count or storage level.
Benefits and examples
An office services company could charge $1 per document for the first 100 documents in a period, then $0.50 for every document after that, using tiered pricing.
A screen-printing company selling custom shirts could charge $10 per shirt, dropping to $9 per shirt across the entire order once a customer buys more than 20, using volume pricing.
A seat-based SaaS product could charge $50 for 1 to 10 seats, $100 for 11 to 20 seats, and $150 for 21 or more seats, using stairstep pricing. A customer with 25 seats and a customer with 50 seats in that same range both pay the flat $150.
A usage-based add-on could include a fixed amount of usage for free, such as a data allowance, and charge only for usage beyond that threshold, combining a quantity-based tier with usage-based billing.
Decimal pricing up to nine decimal places is supported on usage-based and non-usage-based add-on unit prices, which matters when a per-unit rate is a very small fraction of a currency unit.
Frequently asked questions
What is the difference between a plan and an add-on? A plan defines the base subscription price and billing frequency. An add-on is an additional charge layered on top of a plan, priced and configured independently, so a business can offer optional extras without creating a separate plan for every combination.
Can an add-on be required? Yes. Add-ons can be configured as either optional, where the subscriber chooses whether to include them, or required, where every subscriber on that plan gets the add-on automatically.
What pricing models are available for add-ons? Fixed pricing charges a flat rate per period. Tiered pricing charges each unit according to its own tier. Volume pricing charges every unit at the rate of the highest tier reached. Stairstep pricing charges one flat rate for an entire quantity range. Add-ons can also be billed based on usage rather than a fixed quantity.
How is a usage-based add-on different from a quantity-based add-on? A quantity-based add-on such as tiered, volume, or stairstep bills based on a quantity the merchant or subscriber sets directly, such as a number of seats. A usage-based add-on bills based on measured consumption reported over the course of the period, such as API calls or data usage, and is billed in arrears once that usage is known.
Can the same add-on be reused across multiple plans? Yes, if the add-on is derived from an item in a shared item catalog rather than built from scratch on a single plan. That lets a business define an add-on once and attach it consistently to multiple plans instead of recreating it for each one.
How can I see my total add-on revenue? Recurly lets you calculate this from two exports. In the Adjustments export, filter adjustment_type to Charges, invoice_state to Paid, and adjustment_product_code to your add-on codes, then sum adjustment_total. Alternatively, use the Subscription add-ons export and total the subscription_add_on_total_amount_in_cents column.
